1. Field of the Invention
The present invention relates to a method for sewing together separate cover materials to form a trim cover assembly for automotive seat and also to an automotive seat using such trim cover assembly.
2. Description of Prior Art
In general, the process for producing an automotive seat involves the step of securely attaching a trim cover assembly to a foam padding which forms a body of the seat. Some of such trim cover assemblies are formed from a natural leather material (i.e. such animal skin as cow skin or horse skin) or from an artificial leather material.
Both of those natural and artificial leather materials are, however, less elastic or less extendable and relatively high in stiffness. Such non-flexible property has made it difficult to neatly bend a small local part of the material to form a small bent region therein. In other words, two separate cover materials, no matter of whether they may be a natural leather or artificial leather, are sewn together along their respective end portions, forming a seam therealong, with a certain margin to the seam, and then, the two cover materials are folded outwardly and turned over relative to the seam, such that two end portions respective of the sewn two cover materials, which correspond to the said margin, are defined between the two cover materials, projecting inwardly thereof. In that way, a trim cover assembly with a turned-over corner portion is produced, in which the two end portions of cover materials project inwardly thereof and extend along the seam. Normally, such trim cover assembly is securely attached on the surface of foam padding to produce a complete body of automotive seat, such that the corner portion of the trim cover assembly covers a corresponding corner portion of the foam padding.
However, the foregoing inwardly projected end portions of the trim cover assembly contact and erect on the corner portion of foam padding, thus resulting in objectionable irregular protuberant portions being formed on the outer surface of trim cover assembly and also resulting in an undesired sinuous formation of the seam on the corner portion of the trim cover assembly.
Incidentally, some of the automotive seats are provided with side air bags in one or two lateral bolster portions thereof. A trim cover assembly used on such seat is basically formed by sewing together a seating or back support cover section and at least one lateral bolster cover section, wherein the seating or back support cover section is adapted to cover a corresponding foam padding area for supporting a buttocks or back portion of passenger, and the lateral bolster cover section is adapted to cover at least one lateral bolster are of foam padding for supporting one lateral side of the passenger's body including his or her arms. For the purpose of allowing for inflation of the side air bag, a tear-out or breakable portion is defined in a proper region along a seam between the seating cover section and the lateral bolster cover section, with a stay cloth being sewn with a margin given to that seam at a region substantially corresponding to the breakable portion. With this arrangement, upon inflation of the side air bag, the breakable portion is easily broken and opened due to the stay cloth giving an additional force enough to tear away the seam in conjunction with an outwardly expanding force of the inflated side air bag, so that the air bag may protrude through the opened portion and inflate outwardly therefrom. However, such conventional arrangement has been found defective in involving a troublesome step of providing the stay cloth and sewing the same with the trim cover assembly, which in turn makes the trim cover assembly complicated in structure.
In order to avoid the foregoing drawbacks, one can contemplate on trimming away the the end portions of the two cover sections (or two cover materials) corresponding to a margin to seam so as to provide a small margin to be sewn. With this trimming, it is indeed possible to prevent the above-noted formation of irregular protuberant portions on the corner portions of trim cover assembly. But, practically, it is impossible to use a sewing machine to sew together the end portions of two cover sections in such small margin, because the margin given therein is too small for stable and precise sewing by the sewing machine and also can hardly be retained by a retaining member of the sewing machine. As a result thereof, the two cover sections (or two cover materials) can not be sewn together completely, and thus, it is highly possible that the sewn portion or seam between them will be easily teared away and opened, giving a poor appearance of trim cover assembly.